Enhanced Dedicated-Channel Signaling in a CELL_FACH State

ABSTRACT

A new set of random-access preamble signatures are introduced to differentiate new-release UEs from UEs compliant only with earlier releases. Additional new features of a random-access procedure are also disclosed, including an ability to deploy multiple transmission-time-intervals TTIs) in a given area. An example mobile terminal, according to some embodiments of the present invention, selects a TTI from two or more possible TTIs. The mobile terminal then selects a preamble signature from a group of one or more preamble signatures associated with enhanced-uplink resources and associated with the selected TTI, and transmits a random-access channel (RACH) preamble, using the selected preamble signature. In some embodiments, the mobile terminal selects between a 2-millisecond TTI and a 10-millisecond TTI.

BACKGROUND

This application claims the benefit of and priority to U.S. ProvisionalApplication Ser. No. 61/524,131, filed 16 Aug. 2011. The entire contentsof said U.S. Provisional Application are incorporated herein byreference.

BACKGROUND

The 3r^(d)-Generation Partnership Project (3GPP) is continuingdevelopment of the specifications for the Universal Terrestrial RadioAccess Network (UTRAN). More particularly, work is ongoing to improvethe end-user experience and performance in Release 11 of thosespecifications. These efforts include work to improve end-userexperience and system performance in the CELL_FACH state.

CELL_FACH is a Radio Resource Control (RRC) state in which the end-userterminal (user equipment, or UE, in 3GPP terminology) is known on celllevel (i.e., it has a cell ID) and has a layer 2 connection, but has nodedicated physical layer resource. Instead, the UE in CELL_FACH statemust share common physical layer resources with other users in CELL_FACHstate.

The Enhanced Dedicated Channel (E-DCH), which is an uplink packet-accesschannel, can be deployed so that it is may be used by UEs in CELL_FACHstate. More usually, E-DCH is used as a dedicated channel in CELL_DCHstate, in which case a separate resource is allocated for each user.When E-DCH is used in CELL_FACH state, however, the system uses a poolof E-DCH resources that can each be temporarily assigned to a UE inCELL_FACH state.

This common pool of E-DCH resources is referred to herein as “commonE-DCH resources.” E-DCH resources are normally managed by the RadioNetwork Controller (RNC), but the pool of common E-DCH resources isinstead managed by the NodeB (3GPP terminology for a base station.)Configuration data specifying the E-DCH configurations are broadcastedto UEs in the cell.

FIG. 1 illustrates common E-DCH transmission in CELL_FACH state. Shownat the top is the Primary Physical Common Control Channel (P-CCPCH), adownlink physical channel that carries the broadcast control channel(BCH), which in turn carries system- and cell-specific information forUEs, such as indicators that specify which uplink scrambling codes areto be used. The P-CCPCH also serves as a timing reference for allphysical channels.

The next channel illustrated in FIG. 1 is the Acquisition IndicatorChannel (AICH). This physical channel is used to carry AcquisitionIndicators (AIs), which correspond to preamble signatures transmitted byUEs and which are used by the NodeB to acknowledge the receipt ofPhysical Random Access Channel (PRACH) transmissions by UEs. The AICHcan simultaneously acknowledge up to 16 PRACH preambles.

As shown in the next line of FIG. 1, labeled “RACH,” the procedure toaccess the common E-DCH channel in CELL_FACH begins in the same way as aRelease-99 Random Access Channel (RACH), i.e., with preamble powerramping using randomly selected preamble signatures. In the illustratedscenario, the UE transmits a preamble in slots #0 and #3, with thesecond transmission having a higher power level. Having detected thesecond preamble transmission by the UE, the NodeB acknowledges the UE'sPRACH transmission with an AICH sequence, in slot #6. It also informsthe UE which common E-DCH resource it has assigned to the UE. The UE canthen use the E-DCH resource, as shown in FIG. 1, beginning with slot #7.Also shown in FIG. 1 are the Enhanced Absolute Grant Channel (E-AGCH)and the Fractional Dedicated Physical Channel (F-DPCH), which aredownlink channels used to control uplink transmissions. Not shown arethe Enhanced Relative Grant Channel (E-RGCH) and the Enhanced Hybrid-ARQIndicator Channel (E-HICH), which are additional downlink channels forcontrolling the uplink.

A common E-DCH resource is defined as a particular combination of thefollowing: an uplink scrambling code; an E-DCH Radio Network TemporaryIdentifier (E-RNTI); an F-DPCH code and timing offset;E-AGCH/E-RGCH/E-HICH codes and signatures; and parameters for use by theUE in uplink High-Speed Dedicated Physical Control Channel (HS-DPCCH)transmissions, such as power offsets and Channel Quality Reportconfiguration information.

As of Release 10 of the 3GPP standards, the CELL_FACH state is commonlyused to provide an efficient use of radio resources for UEs when data isarriving in bursts, with longer idle periods in between. The goalsinclude both an efficient use of the UE's limited battery resources, aswell as an efficient use of the network's radio resources. Ideally, anUE should be inactive between the bursts but still be capable of swiftlymoving into an active state when there are packets to send or receive.For this kind of on-off type traffic patterns, the connection set-uplatency and signaling load has a significant impact both on thepreservation of the device battery and on the transmission qualityperceived by the end user. In dormant periods, UEs are either sent toIdle state or are set to use configured Discontinuous Receive (DRX)schemes, to save battery.

Information specifying E-DCH resource configurations is broadcasted toUEs using SIB 5, which a system information block sent over the BCH.Some of the broadcasted parameters, such as the Transmission TimeInterval (TTI), are common for all common E-DCH resources.

The specifications for E-DCH as of Release 10 of the 3GPP specificationsare rather rigid and do not allow flexible configurations. One exampleis the Transmission Time Interval (TTI) for common E-DCH resources.Currently, two different TTIs may be configured: either 10-millisecondTTI or 2-millisecond TTI. However, for coverage reasons, the network islikely to have some common E-DCH resources configured with10-millisecond TTI. As specified today, this implies that all resourcesmust the same TTI. However, UEs in good radio conditions, e.g., inso-called hot spots, could make good use of common E-DCH resource with ashorter TTI, i.e. 2 milliseconds. A shorter TTI improves both uplinkthroughput and network capacity, since each resource is occupied forless time. Concurrent deployment of 2-millisecond and 10-millisecond TTIwill thus introduce improvements and provide the network with theflexibility to make an effective and optimal utilization of the commonE-DCH resources.

Another issue with current specifications is that E-DCH operation with2-millisecond TTI does not support per-HARQ activation and de-activationfor those common E-DCH resources. This feature is specified for CELL_DCHstate. Per-HARQ-process activation/de-activation allows the network tokeep a much closer control over the resources and the interferencelevel. Per-HARQ-process activation/de-activation is performed by theNodeB. The problem resides in the fact that the Node-B does not have anexplicit indication of the UE release. If per-HARQ-processactivation/de-activation were to be standardized, there could be aninter-operability issue. If the Node-B sends an HARQactivation/de-activation order to a pre-Release-11 UE, i.e., a UE thatis not compliant to Release 11 specifications, that UE will not act onthat order according the specifications.

The utilization of common E-DCH resources may be inefficient for certaintypes of traffic, especially for very small packets like TCP ACKs. Thisinefficiency arises from the fact that the time from initial RACHpreamble to active transition (the actual time depends on the systemconfiguration) may be prefaced by DPCCH transmission, as well as thatthe relative overhead for a single, small payload transmission is ratherlarge. In other words, the total resources used for control channel andsignaling are relatively high, compared to very small transmissions likea TCP ACK.

Still other inefficiencies arise from the fact that the common E-DCHresource used by a UE is not released until all the HARQ processes havebeen acknowledged. This last issue means that common E-DCH resources areallocated for relatively long periods for the time actually needed forthe transmission. From the network point of view, the network will waitat least one HARQ Round-Trip Time (RTT) from the last acknowledged HARQprocess before it re-uses the resource for another UE. In practice, thismeans that the common E-DCH resource is occupied longer than aResource-99 PRACH resource could be, given that only one packet istransmitted. Furthermore, in high load scenarios, the AICH NACK ratewill increase due to the lack of common E-DCH resources.

To address some of these problems, a fallback approach is beingstandardized. With this approach, a Release-99 RACH process is used toaccess the network, even by Release-11 capable UEs, instead of using oneof the common E-DCH resources. However, a similar problem to one ofthose noted above arises in the deployment of this fallback approach.Namely, the Node-B does not know the UE release. If the network wants toexplicitly indicate to the UE to fall back to RACH using alreadyspecified Release-99 procedures, there will be interoperability issues,since pre-Release-11 UEs will not recognize and act on those orders.Additionally if new procedures are standardized, the NodeB needs to knowwhich UEs are able to handle them.

In brief, the various significant issues with the use of E-DCH inCELL_FACH state include the following: how to control and configure theusage of the concurrent TTI configurations; individual UE capabilitiesare unknown before contention resolution; and network control is neededto handle overall interference, hardware resources, HARQ operationpoint, cell coverage, scheduling, etc.

SUMMARY

In some embodiments of the present invention, a new set of preamblesignatures are introduced to differentiate UEs with new capabilities,e.g., those UEs that are capable of supporting CELL_FACH enhancementsintroduced in Release 11 of the 3GPP standards, from UEs compliant onlywith earlier releases. In addition to using a new set of preamblesignatures that distinguish those UEs capable of performing the new RACHprocedures, embodiments of the present solution include one or moreadditional new features, including an ability to deploy multiple TTIs ina given area, where some of the configured common E-DCH resourcescorrespond to one TTI (e.g., a 2-millisecond TTI) while otherscorrespond to another (e.g., a 10-millisecond TTI). In severalembodiments, this is facilitated by the introduction of a parameter thatspecifies or indicates a bitmap to identify the TTI (e.g., 2-millisecondor 10-millisecond) of each configured common E-DCH resources, such that,for example, each common E-DCH resource is associated with one of thebits in the bitmap and a bit value of 1 indicates one TTI value and abit value of 0 indicates the other TTI value.

An example method, for implementation by a mobile terminal, begins withselecting a transmission-time interval (TTI) from two or more possibleTTIs. The mobile terminal selects a preamble signature from a group ofone or more preamble signatures associated with enhanced-uplinkresources and associated with the selected TTI; and transmits arandom-access channel (RACH) preamble, using the selected preamblesignature. In some embodiments, the mobile terminal selects between a2-millisecond TTI and a 10-millisecond TTI. In several embodiments, themobile terminal first selects a physical random-access channel (PRACH)scrambling code from one or more PRACH scrambling codes available to3GPP Release-11 mobile terminals, in which case the preamble istransmitted using the selected preamble signature and the selected PRACHscrambling code. In some embodiments, broadcast system informationreceived by the mobile terminal specifies groups of preamble signaturesassociated with each of the two or more possible TTIs, for each of theone or more PRACH scrambling codes. In some embodiments, the broadcastsystem information includes a bitmap for each of the one or more PRACHscrambling codes, the bitmap having a bit for each of a plurality ofenhanced-uplink resource configurations, each bit indicating which oftwo possible TTIs is associated with the corresponding enhanced-uplinkresource configuration.

In some cases, the mobile terminal receives an acknowledgement indicatorcorresponding to the selected preamble signature, in which case themobile terminal transmits data using the selected TTI and using anenhanced-uplink resource configuration corresponding to the selectedpreamble signature. In other cases, the mobile terminal receives anegative acknowledgement indicator corresponding to the selectedpreamble signature, but also receives an extended acknowledgementindicator value. In these cases, the mobile terminal transmits datausing an enhanced-uplink resource configuration corresponding to theextended acknowledgement indicator value. Note that this may involvetransmitting data using a TTI other than the selected TTI. Determiningthat a TTI other than the selected TTI is to be used may be based onbroadcasted system information that specifies a mapping between eachuplink resource configuration and a TTI, in some embodiments.

Methods for determining when to fall back to fallback random-accessresources (e.g., Release-99 RACH resources) are also disclosed, and maybe combined with the methods summarized above. In one such method, aftertransmitting a random-access preamble, a mobile terminal receives anegative acknowledgement indicator corresponding to the selectedpreamble signature and receives an extended acknowledgement indicatorvalue, but determines that the received extended acknowledgementindicator value is signaling a fallback to fallback random-accessresources, e.g., a fallback to the legacy random-access procedure andlegacy random-access resources specified by Release 99 of the 3GPPspecifications. The mobile terminal then initiates a fallbackrandom-access procedure, using a preamble signature selected from agroup of one or more preamble signatures corresponding to the fallbackrandom-access resources. In some embodiments, the received extendedacknowledgement indicator value is an indicator value reserved, from aplurality of possible indicator values, to indicate a fallback tofallback random-access resources. As noted above, in some embodimentsthe fallback random-access resources are 3GPP Release-99 random-accessresources and the fallback random-access procedure is a 3GPP Release-99random-access procedure.

Corresponding methods for supporting uplink random-access procedures, ascarried out by a base station, are also disclosed. For instance, onesuch method begins with receiving a random-access channel (RACH)preamble transmitted by a mobile terminal, wherein the RACH preambleuses a preamble signature and a physical random-access channel (PRACH)scrambling code. This is followed by determining which of two or morepossible transmission-time intervals (TTIs) is being requested by themobile terminal, based on the preamble signature and the PRACHscrambling code. Other methods detailed below include methods forsignaling a fallback to fallback random-access resources.

Several of the methods summarized above may be implemented usingelectronic data processing circuitry provided in a mobile terminal.Likewise, others of the methods summarized above may be implementedusing electronic data processing circuitry provided in a base station.Each mobile terminal and base station, of course, also includes suitableradio circuitry for receiving and transmitting radio signals formattedin accordance with known formats and protocols, e.g., Wideband-CDMA andHigh-Speed Packet Access formats and protocols. Accordingly, mobileterminal apparatus and base station apparatus adapted to carry out anyof these techniques are described in detail in the discussion thatfollows.

Of course, the present invention is not limited to the above-summarizedfeatures and advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates common Enhanced Dedicated Channel transmission inCELL_FACH state.

FIG. 2 illustrates a wireless network including a base station and oneor more mobile terminals configured according to the present invention.

FIGS. 3A and 3B illustrate an example method for accessing uplinkresources, according to some embodiments of the present invention.

FIG. 4 illustrates details of the ARQ Indicator Channel.

FIG. 5 is a process flow diagram illustrating an example method asimplemented in a mobile terminal.

FIG. 6 illustrates details of an example method for access uplinkresources according to a fallback random-access procedure.

FIG. 7 is a process flow diagram illustrating an example method asimplemented in a base station.

FIG. 8 is a block diagram illustrating components of a radio node,according to several embodiments of the invention.

FIG. 9 is a block diagram illustrating functional elements of an examplemobile terminal.

FIG. 10 is a block diagram illustrating functional elements of anexample base station.

DETAILED DESCRIPTION

In the discussion that follows, specific details of particularembodiments of the present invention are set forth for purposes ofexplanation and not limitation. It will be appreciated by those skilledin the art that other embodiments may be employed apart from thesespecific details. Furthermore, in some instances detailed descriptionsof well-known methods, nodes, interfaces, circuits, and devices areomitted so as not obscure the description with unnecessary detail. Thoseskilled in the art will appreciate that the functions described may beimplemented in one or in several nodes. Some or all of the functionsdescribed may be implemented using hardware circuitry, such as analogand/or discrete logic gates interconnected to perform a specializedfunction, ASICs, PLAs, etc. Likewise, some or all of the functions maybe implemented using software programs and data in conjunction with oneor more digital microprocessors or general purpose computers. Wherenodes that communicate using the air interface are described, it will beappreciated that those nodes also have suitable radio communicationscircuitry. Moreover, the technology can additionally be considered to beembodied entirely within any form of computer-readable memory, includingnon-transitory embodiments such as solid-state memory, magnetic disk, oroptical disk containing an appropriate set of computer instructions thatwould cause a processor to carry out the techniques described herein.

Hardware implementations of the present invention may include orencompass, without limitation, digital signal processor (DSP) hardware,a reduced instruction set processor, hardware (e.g., digital or analog)circuitry including but not limited to application specific integratedcircuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and(where appropriate) state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors or one or more controllers, and theterms computer, processor, and controller may be employedinterchangeably. When provided by a computer, processor, or controller,the functions may be provided by a single dedicated computer orprocessor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, theterm “processor” or “controller” also refers to other hardware capableof performing such functions and/or executing software, such as theexample hardware recited above.

Referring now to the drawings, FIG. 2 illustrates an exemplary mobilecommunication network 10 for providing wireless communication servicesto mobile terminals 100. Three mobile terminals 100, which are referredto as “user equipment” or “UE” in 3GPP terminology, are shown in FIG. 1.The mobile terminals 100 may comprise, for example, cellular telephones,personal digital assistants, smart phones, laptop computers, handheldcomputers, or other devices with wireless communication capabilities. Itshould be noted that the term “mobile terminal,” as used herein, refersto a terminal operating in a mobile communication network and does notnecessarily imply that the terminal itself is mobile or moveable. Thus,the term may refer to terminals that are installed in fixedconfigurations, such as in certain machine-to-machine applications, aswell as to portable devices, devices installed in motor vehicles, etc.

The mobile communication network 10 comprises a plurality of geographiccell areas or sectors 12. Each geographic cell area or sector 12 isserved by a base station 20, which is referred to in the UTRAN contextas a NodeB. One base station 20 may provide service in multiplegeographic cell areas or sectors 12. The mobile terminals 100 receivesignals from base station 20 on one or more downlink (DL) channels, andtransmit signals to the base station 20 on one or more uplink (UL)channels.

For illustrative purposes, several embodiments of the present inventionwill be described in the context of a UTRAN system. Those skilled in theart will appreciate, however, that several embodiments of the presentinvention may be more generally applicable to other wirelesscommunication systems.

As explained above, as of the Release-10 specifications for UTRAN, someof the common E-DCH parameters are common for all common E-DCHresources. One of those parameters is the E-DCH TTI. Additionally, thesignaling of UE capabilities to the NodeB is limited to the signaling ofa supported release by the selection of PRACH preamble signature to twovalues, which indicate support (or lack thereof) for common E-DCH, i.e.,support of Release-99 or Release-8 capabilities. One aspect of thetechniques presented below is to allow the NodeB to identify a UE'scapability new procedures (e.g., new RACH-related procedures specifiedin Release 11) by associating that capability with a preamble signaturecombined with specific PRACH scrambling codes.

In some embodiments of the present invention, this is done byintroducing a new set of preamble signatures to to differentiate UEswith new capabilities, e.g., those UEs that are capable of supportingCELL_FACH enhancements introduced in Release 11 of the 3GPP standards,from UEs compliant only with earlier releases Note that in the presentdisclosure, those UEs are referred to as “Release 11 UEs.” However, thisterm should be understood as well to refer to UEs that are alsocompliant to later versions of the 3GPP standard and that support theCELL_FACH enhancements described herein.

In addition to using a new set of preamble signatures that distinguishthose UEs capable of performing the new RACH procedures, embodiments ofthe present solution include one or more additional new features,including an ability to deploy multiple TTIs in a given area, where someof the configured common E-DCH resources correspond to one TTI (e.g., a2-millisecond TTI) while others correspond to another (e.g., a10-millisecond TTI). In several embodiments described more fully below,this is facilitated by the introduction of a parameter that specifies orindicates a bitmap to identify the TTI (e.g., 2-millisecond or10-millisecond) of each configured common E-DCH resources, such that,for example, each common E-DCH resource is associated with one of thebits in the bitmap and a bit value of 1 indicates one TTI value and abit value of 0 indicates the other TTI value.

Another aspect of several embodiments of the invention is that there maybe more than one defined PRACH configuration at a time. Accordingly,several sets of parameters, corresponding to several PRACHconfigurations, may be broadcasted by the network as part of the systeminformation in a given cell. Table 1 illustrates an example of theparameters for a PRACH configuration, which include a PRACH scramblingcode, and a set of one or more preamble signatures that are availablefor E-DCH. In addition, an E-DCH TTI bitmap, which maps each commonE-DCH resource to one of at least two possible TTI values, is broadcast.Note that the terms “signature” and “preamble signature” are usedinterchangeably herein. Note also that Table 1 illustrates theparameters for only a single PRACH; similar sets of parameters may bebroadcast for one or more additional PRACH configurations as well. Itshould also be understood that fewer or additional parameters might beused, in various embodiments.

TABLE 1 PRACH Configuration (Rel-11) <1 to maxPRACH>     >PRACHscrambling code     >Signatures available for E-DCH >E-DCH TTI bitmap

The PRACH configuration parameters should be broadcasted as part of thenetwork System Information (SI) by the cell. The configurationparameters are then read from the broadcasted message by a UE operatingin the cell. A UE configured according to the present techniques selectsan appropriate scrambling code configured to signal its releasecapability (e.g. Release-11). The UE also selects an initial TTI, i.e.,a desired TTI, based on the network indications and/or parameters, andbased on the UE's data needs, signal conditions, etc.

Every configured common E-DCH resource is associated with one or severalpreamble signatures per PRACH scrambling code. In the current standards,common E-DCH resources are mapped only by preamble signatures. See,e.g., Section 10.3.6.54a of the 3GPP document “Radio resource control(RRC) protocol specification,” 3GPP TS 25.331, v.10.4.0 (July 2011),available at www.3gpp.org. In embodiments of the present invention, theE-DCH TTI bitmap effectively groups an initially reserved group ofsignatures, i.e., signatures associated with a selected PRACH scramblingcode and available for E-DCH, into two sub-groups, one subgroup ofsignatures associated with common E-DCH resources configured for2-millisecond TTI, and one subgroup of signatures associated with commonE-DCH resources configured for 10-millisecond TTI.

In some embodiments, once the UE has selected the initial TTI (and aPRACH scrambling code, if more than one is available) the UE randomlyselects one signature from the subgroup of signatures associated withthe selected initial TTI. That selected signature is then used toinitiate random access, using previously defined procedures as describedin the background. Note that a systematic selection of the signaturesassociated with the selected TTI, rather than a random selection, may beused in some embodiments.

In some embodiments, the network broadcasts the bitmap indicating whichcommon E-DCH resources use a different TTI from a default TTI. In someembodiments, the NodeB may be configured to dynamically update thebitmap to provide control of the desired TTI configuration at onespecific time, or more generally at specific times. The default TTI inany of these embodiments may be the TTI that is broadcast in the SystemInformation for all common E-DCH resources according to conventionalprocedures. (See Section 10.3.6.9a of the RRC protocol specification3GPP TS 325.331 referred to above.) In some cases, this bitmap consistsof a single bit per each common E-DCH resource. If the bit associatedwith a common E-DCH resource is set to 0, the TTI is the same as thedefault TTI. If the bit is set to 1, it would mean that the TTI isdifferent from the default TTI. If the default TTI is 10 milliseconds,for example, it would mean that the TTI is 2 milliseconds. If thedefault TTI is 2 milliseconds, it would mean that the TTI is 10milliseconds. Of course, the reverse coding of the bit could be used, inother embodiments.

It should be appreciated that the present techniques are independent ofthe techniques used to select a desired TTI. In some cases, a UE mayselect the desired TTI based on signal conditions, data throughputneeds, and/or the like. In other embodiments, if the UE does not havecriteria to select a TTI or if the criteria don't apply to the currentaccess, then a default TTI configuration may be selected.

In some systems configured according to any of these techniques, theNodeB is configured to redirect the attempt of a UE to transmit with aTTI indicated by the UE's random access attempt, in some circumstances,by replying to the UE using an extended Acquisition Indication (E-AI)associated with a common E-DCH resource configured for a TTI other thanthe requested one. For example, if the UE's random access attemptsindicate a 10-millisecond TTI, the Node B may reply to the UE using anE-Al associated with a configuration/common E-DCH resource having a2-millisecond TTI. The UE should then start the transmission using theconfiguration/common E-DCH resource signaled by the Node B and thecorresponding TTI.

In some systems configured according to the present invention, therandom access techniques used above are used to enable handling ofpotential collisions in connection with activating a HS-DPCCH standalonetransmission, which is an uplink transmission of CQI data that separatefrom any ongoing use of E-DCH resources. The NodeB is required to mapthe H-RNTI of the UEs to the E-RNTI. This mapping could be done by theinformation provided by dedicated signaling from RNC to NodeB over thelub interface.

When the NodeB triggers an activation of a HS-DPCCH transmission, e.g.,because of downlink data to be transmitted to the UE when there are noallocated uplink resources, it expects the UE to initiate a randomaccess procedure to acquire an uplink resource and being able totransmit the HS-DPCCH. The random access procedure can be done followingthe above outline enhanced procedure. In case of a collision where twoUEs attempt an access with the same resource, the network can recognizethe colliding UE by the E-RNTI, which will differ from the expectedE-RNTI associated to the H-RNTI of the UE with the activated HS-DPCCH.The colliding UE can then be released by using an “explicit release”procedure, using the E-RNTI present in the MAC-I, but the resource willbe kept in order to serve the HS-DPCCH-activated UE.

Fallback to Release 99 RACH from common E-DCH transmission in IDLE andCELL_FACH sates is an important feature of 3GPP Release 11. Solutionsfor when the fallback to Release 99 RACH procedure takes place can be ofseveral types, either controlled by the NodeB (using, e.g., AICHsignaling) or by the UE itself (based on some suitable criterion), forinstance depending simply on buffer content, configuration or oncontention/load detected on Common E-DCH resources. Several methods forsignaling the fallback to Release-99 PRACH, under the control of aNodeB, are discussed below.

Technique 1

According to previous system specifications, if the network isexperiencing high load due to lack of common E-DCH resources, itcommands the UE to back off and retry after a configurable amount oftime, which is broadcasted in the system information. A similarmechanism can be used to command a UE to fall back to R99 PRACH.

In an example embodiment, such a mechanism works as follows:

-   1. A UE transmits a random access preamble with a signature    allocated/available for common E-DCH access.-   2. A NodeB detects the random access preamble. If no common E-DCH    resources are available, e.g., due to the network experiencing high    load, and/or if the condition to trigger a fall back is met, the    NodeB transmits a grant using AICH/E-AICH as follows:    -   a. AICH value=−1    -   b. E-AICH value=a reserved index to indicate to UE to fall back        to R99 PRACH.        Table 2 illustrates an example of this approach. Note that per        previous standardization the UTRAN network indicates the NACK        for common E-DCH random access via AICH signature ‘0’ and a        positive E-AICH value. In systems and UEs configured according        to some embodiments of the present invention, the same        signature, with a negative E-AICH value can be used to command        the UE fallback to Release 99, as shown in Table 2.

TABLE 2 E-AI Resource Table E-DCH Resource EAI_(s′) Signature_(s)′configuration index +1 0 NACK −1 R99 PRACH Redirect +1 1 (X + 2) mod Y−1 (X + 3) mod Y +1 5 (X + 10) mod Y −1 (X + 11) mod Y +1 6 (X + 12) modY −1 (X + 13) mod Y

(X + 14) mod Y +1 13

−1 (X + 27) mod Y +1 14 (X + 28) mod Y −1 (X + 29) mod Y +1 15 (X + 30)mod Y −1 (X + 31) mod Y

indicates data missing or illegible when filed

Technique 2

A second approach to signalling fallback is described below:

-   1. The network signals new ‘C-EDCH initial access reject max’    parameter in SIB5/SIB5bis as part of ‘Common E-DCH system    information” IE.-   2. In the UE, the new parameter in addition to the existing    parameters is passed from RRC to MAC layer, using the existing    CMAC-Config-REQ.-   3. The UE initiates the preamble transmission using the common E-DCH    signatures.

a. If the UE receives NACK, increment ‘C-EDCH access reject counter’. If‘C-EDCH access reject counter’ >C-EDCH initial access reject max’, thenindicate failure with status ‘C-EDCH access reject threshold.’ In thiscase, the UE shall initiate the fallback to R99 RACH procedure.Otherwise, repeat step 3.

b. If the UE receives an ACK, indicate ready for data transmission tothe higher layers.

FIGS. 3A and 3B together illustrate the existing Enhanced UL CELL_FACHrandom access procedure, but as modified by the present technique. Notethat E indicates the access reject counter, while E_(MAX) indicates themaximum number of access rejections. The portions of the procedureillustrated in FIG. 3 that are modified by the above description areidentified as blocks 310, 320, 330, 340, and 350; specific modificationsare indicated by the underlined text in those blocks.

Technique 3:

In yet another approach, the downlink channel Acquisition IndicatorChannel (AICH) can be used to indicate a redirect to R99 RACH, using theunused part of the AICH slots, i.e., the part with notransmission/reserved for possible future use.

The solution uses up to a maximum of 4 bits to transmit additionalinformation to UE in the AICH channel. FIG. 4 illustrates this approach,where an additional 1 bit (represented by the cross-hatched boxfollowing “a31” in the figure) is transmitted in an AICH slot to signalthe redirect to Release-99 RACH procedures for the Release 11 (or later)UE. The bit can represent either “redirect on”, e.g., with a value of 1,or “redirect off,” e.g., with a value of 0. As it is currently unused,it will be ignored by UEs not compliant with the new specification.

In some systems, then, when the Node B detects a random access preambletransmitted by a UE with a signature associated with common E-DCHaccess, the Node B may use an additional 1 bit in the AICH to signal theUE that it is redirected to Release-99 RACH. Upon receiving theindication from the Node B that it is redirected to Release-99 RACH, theUE then performs a Release-99 random access, i.e., by initiatingtransmission of a random access preamble using a signature associatedindicating Release-99 random access.

Technique 4:

In still another approach, a modification of the existing 3GPP back-offsolution in common E-DCH can be used to signal the fallback toRelease-11 UEs. When a Release-11 UE receives the AICH NACK, it shouldretry the ramping using Release-99 RACH procedures. Once the UE receivesthe NACK, it should transmit immediately the RACH preambles. In someembodiments, this transmission is at the same power level or at a powerlevel close to the power level the UE last used before it received theNACK. This approach is outlined as follows:

-   1. if (AI and E-AI=NACK), and if the UE is Release-11 compliant:

a. do not apply back-off, and

b. start the random access in the next available access slot withP=Pbefore+delta (delta could be negative), using a signature allocatedfor Release 99 RACH procedures.

-   2. else

a. apply back-off as specified in Release 8.

Note that this approach can be viewed as a special case of the approachdescribed above as “Technique 1.” In that first approach, a particularE-AICH value indicates a fallback to Release 99 procedures. In thisapproach (“Technique 4”), an E-AI of NACK triggers the fallbackprocedure.

Technique 5:

In CELL_FACH state, the fallback to R99 RACH will require an autonomousreconfiguration of the L2 layer in UE (fixed to flexible rlc andmac-i/is to mac-c). Note that in Enhanced Uplink CELL_FACH operation,the Signaling Radio Bearers (SRBs) 1, 2, 3, 4, are still configured withfixed size Radio Link Control (RLC). Hence, the UE can transmit uplinkCommon Control Channel (CCCH) messages using Release-99 RACH procedures,without reconfiguring the RLC layer in case of fallback to R99 RACH.

According to this fifth approach, the network-controlled fallback toRelease-99 RACH′ works as follows:

-   1. The network indicates UE to redirect to R99 RACH.-   2. UE initiates a cell update procedure with a new cause value (e.g.    ‘common E-DCH resource unavailable ’) via SRB 2 (fixed-size RLC,    using uplink CCCH messages) and configuring the MAC as per the PRACH    information provided in the System broadcast.-   3. The Network (RNC) on reception of cell update with the new cause    value, shall decide to up switch the UE to CELL_DCH or    CELL_FACH(RACH/FACH), based on the ongoing traffic volume    measurements via cell update confirm message.

The process flow diagram of FIG. 5 illustrates a generalized method foraccessing uplink resources in a wireless network according to several ofthe techniques described above. This method, which is suitable forimplementation by a mobile terminal (e.g., a UE compliant with theforthcoming 3GPP Release 11 standards), is applicable in a wirelessnetwork that supports an enhanced-uplink random-access procedure foraccessing enhanced-uplink resources, as in the common E-DCH resourcesdiscussed above, and a fallback random-access procedure for access tofallback random-access resources, such as Release-99 RACH resources.

As shown at block 510, the method begins with selecting a TTI from twoor more possible TTIs, such as between a 2-millisecond TTI and a10-millisecond TTI. Next, as shown at block 520, a preamble signature isselected, from a group of one or more preamble signatures associatedwith enhanced-uplink resources and associated with the selected TTI.Next, as shown at block 530, a random-access channel (RACH) preamble istransmitted, using the selected preamble signature.

Although not shown in the process flow of FIG. 5, the illustratedtechnique may be preceded by the selection of a physical random-accesschannel (PRACH) scrambling code from one or more PRACH scrambling codesallocated to 3GPP Release-11 mobile terminals. The RACH preamble istransmitted using the selected preamble signature and the selected PRACHscrambling code. In some cases, the mobile terminal will receivebroadcast system information specifying groups of preamble signaturesassociated with each of the two or more possible TTIs, for each of theone or more PRACH scrambling codes allocated to Release-11 mobileterminals. Again, it should be understand that “Release-11 mobileterminal” is meant here to refer to any mobile terminal that iscompliant with Release 11 standard, including those that are alsocompliant with one or more subsequent releases.

The broadcast system information received by the mobile terminal may insome cases comprise a bitmap for each of the one or more PRACHscrambling codes. This bitmap has bit for each of a plurality ofenhanced-uplink resource configurations, each bit indicating which oftwo possible TTIs is associated with the corresponding enhanced-uplinkresource configuration. The mobile terminal uses the bitmap to dividethe enhanced-uplink resource configurations into two groups, associatedwith the possible TTIs. Because each preamble signature is associatedwith an enhanced-uplink resource configuration, this bitmap also servesto divide the available preamble signatures into two groups, againassociated with corresponding TTIs. The mobile terminal selects apreamble signature from the appropriate group. Note that in some casesthe bitmap may differ from one scrambling code to another, while inothers a single bitmap applies to all scrambling codes.

FIG. 6 illustrates another process flow for implementation by a mobileterminal, in this case illustrating an example approach to facilitatinga fallback to a fallback random-access procedure using fallbackrandom-access resources. Note that the process illustrated in FIG. 6 maybe combined with the process illustrated in FIG. 5.

The illustrated process begins, as shown at block 605, with thetransmission of a PRACH preamble, using an appropriately selectedpreamble signature corresponding to an enhanced-uplink resource. Itshould be appreciated that this preamble signature may be selectedaccording to the process illustrated in FIG. 5, in some embodiments, inwhich case the operation illustrated at block 605 corresponds directlyto the operation shown at block 530 of FIG. 5.

After transmitting the preamble signature, the mobile terminal monitorsthe acknowledgement indicator channel (AICH) for an acknowledgeindicator. If neither an AICH ACK nor an AICH NACK is received inresponse (see blocks 610 and 630), then the preamble transmission poweris increased, as shown at block 640, and repeated. If an AICH ACK isreceived, then the mobile terminal transmits data on the enhanced-uplinkresource that corresponds to the transmitted preamble signature, asshown at block 620, using the corresponding TTI.

If an AICH NACK is received, on the other hand, the mobile terminalreceives and evaluates an extended acknowledgement indicator value, asshown at block 650. In some instances the extended acknowledgementindicator value will indicate a fallback (redirection) to a fallbackrandom-access procedure, as seen at block 660. For example, the receivedextended acknowledgement indicator value may be an indicator valuereserved, from a plurality of possible indicator values, to indicate afallback to fallback random-access resources. In this case, the mobileterminal initiates a fallback random-access procedure, using a preamblesignature selected from a group of one or more preamble signaturescorresponding to the fallback random-access resources.

In other instances, the extended acknowledgement indicator value willinstead point to an enhanced-uplink resource configuration, in whichcase the mobile terminal proceeds by transmitting data using theenhanced-uplink resource configuration corresponding to the extendedacknowledgement indicator value. Note that in some cases thisenhanced-uplink resource configuration may correspond to a TTI otherthan the TTI initially selected by the mobile terminal. As discussedearlier, in some embodiments this may be determined by consultingbroadcasted system information that specifies a mapping between eachuplink resource configuration and a TTI, e.g., a bitmap that indicateswhich uplink resource configurations correspond to each possible TTI.

Of course, the fallback random-access resources in the processillustrated in FIG. 6 may be 3GPP Release-99 random-access resources,and the fallback random-access procedure a 3GPP Release-99 random-accessprocedure, in some embodiments. The illustrated approach may be appliedto other systems, however.

The process flow diagram of FIG. 7 illustrates a method, implemented bya base station, which complements the mobile terminal-based methods ofFIGS. 5 and 6. As seen at block 710, the illustrated method forsupporting uplink random-access procedures begins with receiving arandom-access channel (RACH) preamble transmitted by a mobile terminal,where the RACH preamble uses a preamble signature and a physicalrandom-access channel (PRACH) scrambling code. As seen at block 720, themethod continues with the determination of which of two or more possibletransmission-time intervals (TTIs) is being requested by the mobileterminal, based on the preamble signature and the PRACH scrambling code.

The possible TTIs may consist of two-millisecond TTI and aten-millisecond TTI, in some embodiments. Although this operation is notpictured in FIG. 7, the illustrated process may be preceded by thetransmitting of system information specifying a group of preamblesignatures for each of the two or more possible TTIs, for each of one ormore physical random-access channel (PRACH) scrambling codes. In somecases, this system information may include a bitmap having a bit foreach of a plurality of enhanced-uplink resource configurations, each bitindicating which of two possible TTIs is associated with thecorresponding enhanced-uplink resource configuration.

Steps taken by the base station after the preamble is received anddecoded will depend, for example, on the available resources. Severalresponses by the base station are possible. In some cases, the basestation will choose to grant the mobile terminal's request for aspecific enhanced-uplink resource. In these cases, the base stationtransmits an acknowledgement indicator corresponding to the preamblesignature, and subsequently receives data transmitted by the mobileterminal, using the requested TTI and using an enhanced-uplink resourceconfiguration corresponding to the preamble signature.

In other cases, the base station will refer the mobile terminal toanother enhanced-uplink resource, possibly one corresponding to a TTIother than requested. In these cases, the base station transmits anegative acknowledgement indicator corresponding to the preamblesignature and transmits an extended acknowledgement indicator valuecorresponding to an enhanced-uplink resource configuration, after whichit receives data transmitted by the mobile terminal using theenhanced-uplink resource configuration.

In still other cases, a base station configured according to someembodiments of the present invention will redirect the mobile terminalto a fallback random-access procedure, e.g., the Release-99 RACHprocedure. In these cases, the base station transmits a negativeacknowledgement indicator corresponding to the selected preamblesignature and transmits a particular extended acknowledgement indicatorvalue that signals a fallback to fallback random-access resources.Subsequently, the base station receives a fallback random-accesspreamble transmitted by the mobile terminal, the fallback random-accesspreamble using a preamble signature selected from a group of one or morepreamble signatures corresponding to the fallback random-accessresources.

The operations illustrated in the process flow diagrams of FIGS. 5 and 6may be implemented using electronic data processing circuitry providedin the mobile terminal. Likewise, the operations in the flowchart ofFIG. 7 may be implemented using electronic data processing circuitryprovided in a base station. Each mobile terminal and base station, ofcourse, also includes suitable radio circuitry for receiving andtransmitting radio signals formatted in accordance with known formatsand protocols, such as the formats and protocols specified by 3GPP forUTRAN.

FIG. 8 illustrates features of an example communications node 1500according to several embodiments of the present invention. Although thedetailed configuration, as well as features such as physical size, powerrequirements, etc., will vary, the general characteristics of theelements of communications node 1500 are common to both a wireless basestation and a mobile terminal. Further, both may be adapted to carry outone or several of the techniques described above for managing and accessuplink resources in a wireless network.

Communications node 1500 comprises a transceiver 1520 for communicatingwith mobile terminals (in the case of a base station) or with one ormore base stations (in the case of a mobile terminal) as well as aprocessing circuit 1510 for processing the signals transmitted andreceived by the transceiver 1520. Transceiver 1520 includes atransmitter 1525 coupled to one or more transmit antennas 1528 andreceiver 1530 coupled to one or more receive antennas 1533. The sameantenna(s) 1528 and 1533 may be used for both transmission andreception. Receiver 1530 and transmitter 1525 use known radio processingand signal processing components and techniques, typically according toa particular telecommunications standard such as the 3GPP standards forWideband CDMA (W-CDMA) and High-Speed Packet Access (HSPA). Because thevarious details and engineering tradeoffs associated with the design andimplementation of such circuitry are well known and are unnecessary to afull understanding of the invention, additional details are not shownhere.

Processing circuit 1510 comprises one or more processors 1540, hardware,firmware or a combination thereof, coupled to one or more memory devices1550 that make up a data storage memory 1555 and a program storagememory 1560. Memory 1550 may comprise one or several types of memorysuch as read-only memory (ROM), random-access memory, cache memory,flash memory devices, optical storage devices, etc. Again, because thevarious details and engineering tradeoffs associated with the design ofbaseband processing circuitry for mobile devices and wireless basestations are well known and are unnecessary to a full understanding ofthe invention, additional details are not shown here.

Typical functions of the processing circuit 1510 include modulation andcoding of transmitted signals and the demodulation and decoding ofreceived signals. In several embodiments of the present invention,processing circuit 1510 is adapted, using suitable program code storedin program storage memory 1560, for example, to carry out one of thetechniques described above for accessing uplink resources from a mobileterminal or for supporting uplink random-access procedures in a basestation. Of course, it will be appreciated that not all of the steps ofthese techniques are necessarily performed in a single microprocessor oreven in a single module.

FIG. 9 illustrates several functional elements of a mobile terminal1600, adapted to carry out some of the techniques discussed in detailabove. Mobile terminal 1600 includes a TTI selection circuit 1610configured to select a TTI from two or more possible TTIs, and apreamble signature selection circuit 1620 configured to select apreamble signature from a group of one or more preamble signaturesassociated with enhanced-uplink resources and associated with theselected TTI. Mobile terminal 1600 further includes a transmit controlcircuit 1630, which is configured to control transmitter circuit 1640 totransmit a random-access channel preamble, using the selected preamblesignature. In the pictured example, TTI selection circuit 1610, preamblesignature selection circuit 1620, and transmit control circuit 1630,make up part of an uplink processing circuit 1650, which may beconfigured in the same manner as processing circuit 1510 in FIG. 8.Likewise, transmitter 1640 circuit, along with receiver circuit 1660,makes up part of transceiver 1670.

Similarly, FIG. 10 illustrates several functional elements of an examplebase station 1000, adapted to carry out some of the techniques discussedin detail above. Base station 1000 includes a transceiver 1060, which inturn includes a receiver circuit 1010 and a transmitter circuit 1050.Base station 1000 further includes a processing circuit 1020, which inturn includes a baseband processing circuit 1030 configured to receive aRACH preamble received from a mobile terminal via receiver circuit 1010and an E-DCH resource manager that determines which TTI is requested bythe mobile terminal, based on the preamble signature and scrambling codeused by the mobile terminal in forming the RACH preamble. As discussedin detail above, the E-DCH resource manager may then choose to grant anE-DCH resource in response, or to trigger a fallback to R99random-access resources. Note that processing circuit 1020 may beconfigured in the same manner as processing circuit 1510 in FIG. 8.

Accordingly, in various embodiments of the invention, processingcircuits, such as the processing circuit 1510 in FIG. 8, the uplinkprocessing circuit 1650 in FIG. 9, and the processing circuit 1020 inFIG. 10, are configured to carry out one or more of the techniquesdescribed in detail above. Likewise, other embodiments include mobileterminals and base stations including one or more such processingcircuits. In some cases, these processing circuits are configured withappropriate program code, stored in one or more suitable memory devices,to implement one or more of the techniques described herein. Of course,it will be appreciated that not all of the steps of these techniques arenecessarily performed in a single microprocessor or even in a singlemodule.

Examples of several embodiments of the present invention have beendescribed in detail above, with reference to the attached illustrationsof specific embodiments. Because it is not possible, of course, todescribe every conceivable combination of components or techniques,those skilled in the art will appreciate that the present invention canbe implemented in other ways than those specifically set forth herein,without departing from essential characteristics of the invention.Modifications and other embodiments of the disclosed invention(s) willcome to mind to one skilled in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. Therefore, it is to be understood that the invention(s) is/arenot to be limited to the specific embodiments disclosed and thatmodifications and other embodiments are intended to be included withinthe scope of this disclosure. Although specific terms may be employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation. The present embodiments are thus to beconsidered in all respects as illustrative and not restrictive.

What is claimed is:
 1. A method, in a mobile terminal, for accessinguplink resources in a wireless network that supports an enhanced-uplinkrandom-access procedure for accessing enhanced-uplink resources and afallback random-access procedure for access to fallback random-accessresources, the method comprising: selecting a transmission-time interval(TTI) from two or more possible TTIs; selecting a preamble signaturefrom a group of one or more preamble signatures associated withenhanced-uplink resources and associated with the selected TTI; andtransmitting a random-access channel (RACH) preamble, using the selectedpreamble signature.
 2. The method of claim 1, wherein selecting the TTIcomprises selecting between a 2-millisecond TTI and a 10-millisecondTTI.
 3. The method of claim 1, further comprising first selecting aphysical random-access channel (PRACH) scrambling code from one or morePRACH scrambling codes allocated to 3GPP Release-11 mobile terminals,wherein said RACH preamble is transmitted using the selected preamblesignature and the selected PRACH scrambling code.
 4. The method of claim3, further comprising first receiving broadcast system informationspecifying groups of preamble signatures associated with each of the twoor more possible TTIs, for each of the one or more PRACH scramblingcodes.
 5. The method of claim 4, wherein the broadcast systeminformation comprises a bitmap for each of the one or more PRACHscrambling codes, the bitmap having a bit for each of a plurality ofenhanced-uplink resource configurations, each bit indicating which oftwo possible TTIs is associated with the corresponding enhanced-uplinkresource configuration.
 6. The method of claim 1, further comprising:receiving an acknowledgement indicator corresponding to the selectedpreamble signature; and transmitting data using the selected TTI andusing an enhanced-uplink resource configuration corresponding to theselected preamble signature.
 7. The method of claim 1, furthercomprising: receiving a negative acknowledgement indicator correspondingto the selected preamble signature; receiving an extendedacknowledgement indicator value; and transmitting data using anenhanced-uplink resource configuration corresponding to the extendedacknowledgement indicator value.
 8. The method of claim 7, wherein saidtransmitting data is performed using a TTI other than the selected TTI.9. The method of claim 8, further comprising determining that a TTIother than the selected TTI is to be used based on broadcasted systeminformation that specifies a mapping between each uplink resourceconfiguration and a TTI.
 10. The method of claim 1, further comprising:receiving a negative acknowledgement indicator corresponding to theselected preamble signature; receiving an extended acknowledgementindicator value; determining that the received extended acknowledgementindicator value is signaling a fallback to fallback random-accessresources; and initiating a fallback random-access procedure, using apreamble signature selected from a group of one or more preamblesignatures corresponding to the fallback random-access resources. 11.The method of claim 10, wherein the fallback random-access resources are3GPP Release-99 random-access resources and the fallback random-accessprocedure is a 3GPP Release-99 random-access procedure.
 12. The methodof claim 11, wherein the received extended acknowledgement indicatorvalue is an indicator value reserved, from a plurality of possibleindicator values, to indicate a fallback to fallback random-accessresources.
 13. A method, in a base station, for supporting uplinkrandom-access procedures, the method comprising: receiving arandom-access channel (RACH) preamble transmitted by a mobile terminal,wherein the RACH preamble uses a preamble signature and a physicalrandom-access channel (PRACH) scrambling code; and determining which oftwo or more possible transmission-time intervals (TTIs) is beingrequested by the mobile terminal, based on the preamble signature andthe PRACH scrambling code.
 14. The method of claim 13, wherein the twoor more possible TTIs consist of a 2-millisecond TTI and a10-millisecond TTI.
 15. The method of claim 13, further comprising firsttransmitting system information specifying a group of preamblesignatures for each of the two or more possible TTIs, for each of one ormore physical random-access channel (PRACH) scrambling codes.
 16. Themethod of claim 15, wherein the broadcast system information for each ofthe PRACH scrambling codes comprises a bitmap having a bit for each of aplurality of enhanced-uplink resource configurations, each bitindicating which of two possible TTIs is associated with thecorresponding enhanced-uplink resource configuration.
 17. The method ofclaim 13, further comprising: transmitting an acknowledgement indicatorcorresponding to the preamble signature; and receiving data transmittedby the mobile terminal, wherein said data is transmitted using therequested TTI and using an enhanced-uplink resource configurationcorresponding to the preamble signature.
 18. The method of claim 13,further comprising: transmitting a negative acknowledgement indicatorcorresponding to the preamble signature; transmitting an extendedacknowledgement indicator value corresponding to an enhanced-uplinkresource configuration; and receiving data transmitted by the mobileterminal, wherein said data is transmitted using the enhanced-uplinkresource configuration.
 19. The method of claim 18, wherein theenhanced-uplink resource configuration corresponds to a TTI other thanthe TTI requested by the mobile terminal.
 20. The method of claim 13,further comprising: transmitting a negative acknowledgement indicatorcorresponding to the selected preamble signature; transmitting anextended acknowledgement indicator value, wherein said extendedacknowledgement indicator value signals a fallback to fallbackrandom-access resources; and receiving a fallback random-access preambletransmitted by the mobile terminal, wherein the fallback random-accesspreamble uses a preamble signature selected from a group of one or morepreamble signatures corresponding to the fallback random-accessresources.
 21. The method of claim 20, wherein the fallbackrandom-access are 3GPP Release-99 random-access resources and thefallback random-access preamble signature is a preamble signatureassociated with 3GPP Release-99 random-access resources.
 22. The methodof claim 20, wherein the transmitted extended acknowledgement indicatorvalue is an indicator value reserved, from a plurality of possibleindicator values, to indicate a fallback to fallback random-accessresources.
 23. A method, in a mobile terminal, for accessing uplinkresources in a wireless network that supports an enhanced-uplinkrandom-access procedure for accessing enhanced-uplink resources and afallback random-access procedure for access to fallback random-accessresources, the method comprising: selecting a preamble signature from agroup of one or more preamble signatures associated with enhanced-uplinkresources; transmitting a random-access channel (RACH) preamble, usingthe selected preamble signature; receiving a negative acknowledgementindicator corresponding to the selected preamble signature; receiving anextended acknowledgement indicator value; determining that the receivedextended acknowledgement indicator value is signaling a fallback tofallback random-access resources; and initiating a fallbackrandom-access procedure, using a preamble signature selected from agroup of one or more preamble signatures corresponding to the fallbackrandom-access resources.
 24. The method of claim 23, wherein thereceived extended acknowledgement indicator value is an indicator valuereserved, from a plurality of possible indicator values, to indicate afallback to fallback random-access resources.
 25. A method, in a basestation, for supporting uplink random-access procedures in a wirelessnetwork that supports an enhanced-uplink random-access procedure foraccessing enhanced-uplink resources and a fallback random-accessprocedure for access to fallback random-access resources, the methodcomprising: receiving a random-access channel (RACH) preambletransmitted by a mobile terminal, wherein the RACH preamble uses a firstpreamble signature and a first physical random-access channel (PRACH)scrambling code, the first preamble signature corresponding to enhanceduplink random-access resources ; transmitting a negative acknowledgementindicator corresponding to the first preamble signature; transmitting anextended acknowledgement indicator value, wherein said extendedacknowledgement indicator value signals a fallback to fallbackrandom-access resources; and receiving a fallback random-access preambletransmitted by the mobile terminal, wherein the fallback random-accesspreamble uses a preamble signature selected from a group of one or morepreamble signatures corresponding to the fallback random-accessresources.
 26. The method of claim 25, wherein the transmitted extendedacknowledgement indicator value is an indicator value reserved, from aplurality of possible indicator values, to indicate a fallback tofallback random-access resources.
 27. A mobile terminal configured toaccess uplink resources in a wireless network that supports anenhanced-uplink random-access procedure for accessing enhanced-uplinkresources and a fallback random-access procedure for access to fallbackrandom-access resources, the mobile terminal comprising a radiotransceiver and a processing circuit configured to: select atransmission-time interval (TTI) from two or more possible TTIs; selecta preamble signature from a group of one or more preamble signaturesassociated with enhanced-uplink resources and associated with theselected TTI; and control the radio transceiver to transmit arandom-access channel (RACH) preamble, using the selected preamblesignature.
 28. The mobile terminal of claim 27, wherein the processingcircuitry is further configured to first select a physical random-accesschannel (PRACH) scrambling code from one or more PRACH scrambling codesallocated to 3GPP Release-11 mobile terminals and to control the radiotransceiver to transmit the RACH preamble using the selected preamblesignature and the selected PRACH scrambling code.
 29. The mobileterminal of claim 28, wherein the processing circuit is furtherconfigured to first receive, via the radio transceiver, broadcast systeminformation specifying groups of preamble signatures associated witheach of the two or more possible TTIs, for each of the one or more PRACHscrambling codes.
 30. The mobile terminal of claim 27, wherein theprocessing circuit is further configured to: receive a negativeacknowledgement indicator corresponding to the selected preamblesignature, via the radio transceiver; receive an extendedacknowledgement indicator value, via the radio transceiver; and controlthe radio transmitter to transmit data using an enhanced-uplink resourceconfiguration corresponding to the extended acknowledgement indicatorvalue.
 31. The mobile terminal of claim 30, wherein the processingcircuit is further configured to determine that a TTI other than theselected TTI is to be used, based on broadcasted system information thatspecifies a mapping between each uplink resource configuration and aTTI, and to control the radio transmitter to transmit the data using aTTI other than the selected TTI.
 32. The mobile terminal of claim 27,wherein the processing circuit is further configured to: receive anegative acknowledgement indicator corresponding to the selectedpreamble signature, via the radio transceiver; receive an extendedacknowledgement indicator value, via the radio transceiver; determinethat the received extended acknowledgement indicator value is signalinga fallback to fallback random-access resources, wherein the receivedextended acknowledgement indicator value is an indicator value reserved,from a plurality of possible indicator values, to indicate a fallback tofallback random-access resources; and initiate a fallback random-accessprocedure, using a preamble signature selected from a group of one ormore preamble signatures corresponding to the fallback random-accessresources.
 33. A base station configured to support uplink random-accessprocedures, the base station comprising a radio transceiver andprocessing circuitry configured to: receive, via the radio transceiver,a random-access channel (RACH) preamble transmitted by a mobileterminal, wherein the RACH preamble uses a preamble signature and aphysical random-access channel (PRACH) scrambling code; and determinewhich of two or more possible transmission-time intervals (TTIs) isbeing requested by the mobile terminal, based on the preamble signatureand the PRACH scrambling code.
 34. The base station of claim 33, whereinthe processing circuitry is further configured to first control theradio transceiver to transmit system information specifying a group ofpreamble signatures for each of the two or more possible TTIs, for eachof one or more physical random-access channel (PRACH) scrambling codes.35. The base station of claim 33, wherein the processing circuitry isfurther configured to: control the radio transceiver to transmit anacknowledgement indicator corresponding to the preamble signature; andreceive, via the radio transceiver, data transmitted by the mobileterminal, wherein said data is transmitted using the requested TTI andusing an enhanced-uplink resource configuration corresponding to thepreamble signature.
 36. The base station of claim 33, wherein theprocessing circuitry is further configured to: control the radiotransceiver to transmit a negative acknowledgement indicatorcorresponding to the preamble signature; control the radio transceiverto transmit an extended acknowledgement indicator value corresponding toan enhanced-uplink resource configuration, wherein the enhanced-uplinkresource configuration corresponds to a TTI other than the TTI requestedby the mobile terminal; and receive, via the radio transceiver, datatransmitted by the mobile terminal, wherein said data is transmittedusing the enhanced-uplink resource configuration.
 37. The base stationof claim 33, wherein the processing circuitry is further configured to:control the radio transceiver to transmit a negative acknowledgementindicator corresponding to the selected preamble signature; control theradio transceiver to transmit an extended acknowledgement indicatorvalue, wherein said extended acknowledgement indicator is an indicatorvalue reserved, from a plurality of possible indicator values, toindicate a fallback to fallback random-access resources; and receive,via the radio transceiver, a fallback random-access preamble transmittedby the mobile terminal, wherein the fallback random-access preamble usesa preamble signature selected from a group of one or more preamblesignatures corresponding to the fallback random-access resources.
 38. Amobile terminal configured to access uplink resources in a wirelessnetwork that supports an enhanced-uplink random-access procedure foraccessing enhanced-uplink resources and a fallback random-accessprocedure for access to fallback random-access resources, the mobileterminal comprising a radio transceiver and processing circuitryconfigured to: select a preamble signature from a group of one or morepreamble signatures associated with enhanced-uplink resources; controlthe radio transceiver to transmit a random-access channel (RACH)preamble, using the selected preamble signature; receive, via the radiotransceiver, a negative acknowledgement indicator corresponding to theselected preamble signature; receive, via the radio transceiver, anextended acknowledgement indicator value; determine that the receivedextended acknowledgement indicator value is signaling a fallback tofallback random-access resources; and initiate a fallback random-accessprocedure, using a preamble signature selected from a group of one ormore preamble signatures corresponding to the fallback random-accessresources.
 39. The method of claim 23, wherein the received extendedacknowledgement indicator value is an indicator value reserved, from aplurality of possible indicator values, to indicate a fallback tofallback random-access resources.
 40. A base station configured tosupport uplink random-access procedures in a wireless network thatsupports an enhanced-uplink random-access procedure for accessingenhanced-uplink resources and a fallback random-access procedure foraccess to fallback random-access resources, the base station comprisinga radio transceiver and processing circuitry configured to: receive, viathe radio transceiver, a random-access channel (RACH) preambletransmitted by a mobile terminal, wherein the RACH preamble uses a firstpreamble signature and a first physical random-access channel (PRACH)scrambling code, the first preamble signature corresponding to enhanceduplink random-access resources ; control the radio transceiver totransmit a negative acknowledgement indicator corresponding to the firstpreamble signature; control the radio transceiver to transmit anextended acknowledgement indicator value, wherein the transmittedextended acknowledgement indicator value is an indicator value reserved,from a plurality of possible indicator values, to indicate a fallback tofallback random-access resources; and receive, via the radiotransceiver, a fallback random-access preamble transmitted by the mobileterminal, wherein the fallback random-access preamble uses a preamblesignature selected from a group of one or more preamble signaturescorresponding to the fallback random-access resources.